1. Field of the Invention
The present invention relates to a piston for a reciprocating machine and to a reciprocating machine using the piston.
2. Description of the Related Art
Reciprocating machines include a swash plate compressor, and this type of compressor is disclosed, for example, in Unexamined Japanese Patent Publication No. H06-346844. The compressor disclosed in this publication comprises a drive shaft to be rotated and a cylinder block arranged coaxially with the drive shaft and having a plurality of cylinder bores formed therein. The cylinder bores are arranged around the axis of the drive shaft at regular intervals and extend parallel with the axis of the drive shaft. A piston is fitted into each of the cylinder bores.
The compressor further comprises a rear case constituting a housing of the compressor in cooperation with the cylinder block and having a crank chamber defined therein. A swash plate is arranged in the crank chamber. The swash plate is coupled to the drive shaft at a predetermined angle to the axis of the drive shaft and is rotatable together with the drive shaft. The outer peripheral edge of the swash plate is engaged with each piston through a pair of shoes.
As the drive shaft is rotated together with the swash plate, rotation of the swash plate is converted to reciprocating motion of each piston through the shoes. In the case of the swash plate compressor, the reciprocating motion of the piston causes a suction process for sucking a fluid, that is, a refrigerant gas, into a pressure chamber defined in the cylinder bore, a compression process for compressing the refrigerant gas in the pressure chamber, and a discharge process for discharging the refrigerant gas from the pressure chamber.
The aforementioned pair of shoes is disposed such that the shoes merely slidably hold the outer peripheral edge of the swash plate therebetween, and accordingly, the piston can possibly rotate about an axis thereof within the cylinder bore.
To prevent such rotation, the piston disclosed in the abovementioned publication has a stopper surface. When the piston reciprocates, the stopper surface slides on the inner surface of the crank chamber in the reciprocating direction of the piston, to prevent rotation of the piston about its axis.
During operation of the compressor, the stopper surface of the piston is always brought into sliding contact with the inner surface of the crank chamber, and therefore, the sliding resistance of the piston, namely, the power consumption of the compressor, increases. Further, if excessive stress acts on the stopper surface or the supply of lubricating oil to the stopper surface is insufficient, adhesion or seizure of the stopper surface to the inner surface of the crank chamber may possibly be caused.